Method and apparatus for performing mobility measurements in a communication network

ABSTRACT

A method and apparatus for performing mobility measurement in a communication network ( 100 ) is described. The method includes of receiving a subframe sequence pattern from a node in the communication network ( 100 ). The subframe sequence pattern indicates types of subframes being transmitted by a neighboring cell node ( 104 ) in a neighboring cell ( 112 ). The method includes receiving a subframe from a sequence of subframes transmitted by the neighboring cell node ( 104 ) in the neighboring cell ( 112 ), and determining that the received subframe is a multicast subframe based on the subframe sequence pattern. The method then includes performing a single cell-specific reference symbol measurement in response to determining that the received subframe is the multicast subframe.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication network andmore particularly to perform mobility measurements in a communicationnetwork.

BACKGROUND

In a wireless communication network, communication is establishedbetween a node and a plurality of mobile devices. Typically,communication is established over a link known as an uplink/downlink forcommunicating data between the node and a mobile device. However, such alink weakens as the mobile device travels to the edge of a cell or toanother cell, and as a result the mobile device may have discontinuouscommunication with the node. The mobile device therefore establishes anew link with a node in a neighboring cell when the mobile device tendsto travel to the corresponding neighboring cell. The mobile devicehowever, prior to establishing such a new link, performs mobilitymeasurement on one or more of the neighboring cells. Such measurementmay be a general measurement of a total power received from atransmitter of the node located at the neighboring cell.

Upon performing mobility measurement on the neighboring cells, themobile device selects a cell, or makes a report to facilitate selectionof a cell, that has an optimized communication configuration. Forexample, the selected cell may have a maximum power level and so is thebest neighboring cell to provide uninterrupted or continuouscommunication between the node and the mobile device.

In the existing technique, the mobile device receives unicast subframesfrom each node in the neighboring cells and performs mobilitymeasurements over such received unicast subframes. The mobilitymeasurement is for only unicast subframes as only one type oftransmission known as unicast transmission occurs in the communicationnetwork. However, the technology has been upgraded and in some instance,the neighboring cell may support both unicast and multicast subframetransmission, or hybrid combinations thereof. Multicast subframesinclude subframes comprising both unicast and multicast components, butat least a portion of the subframe is transmitted in a multicastfashion. Observations of a transmission, e.g., multicast transmission,in which multiple neighboring cells are participating, does notgenerally enable the mobile device to identify a specific individual andoptimal neighboring cell, and indeed can lead to erroneous mobilitymeasurement when such observations are treated as unicast observations.However, in a conservative measurement strategy, all transmissionscomprising, in part, multicast transmissions, are neglected by themobile device during mobility measurement. Such negligence may lead toincreased mobile device mobility measurement activity and ultimately tohigher power consumption by the mobile device when seeking to maintainspecified mobility measurement accuracy, or to a loss of measurementaccuracy. Thus, there is a need for the mobile device to performmobility measurements for any type of subframe received in thecommunication network.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, together with the detailed description below, are incorporated inand form part of the specification, and serve to further illustrateembodiments of concepts that include the claimed invention, and explainvarious principles and advantages of those embodiments.

FIG. 1 is a system diagram of a communication network in accordance withsome embodiments.

FIG. 2 is a block diagram of a multi-level framing structure inaccordance with some embodiments.

FIG. 3 is a block diagram of a mobile device in accordance with someembodiments.

FIG. 4 is flowchart of a method for performing mobility measurements ina communication network based on a subframe sequence pattern inaccordance with some embodiments.

FIG. 5 is a flow chart of a method for determining a type of subframereceived based on the subframe sequence pattern in accordance with someembodiments.

FIG. 6 is a flowchart of a method for performing mobility measurementsin a communication network based on a single bit signal in accordancewith some embodiments.

FIG. 7 is a flow chart of a method for determining a type of subframereceived based on the single bit signal in accordance with someembodiments.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

The apparatus and method components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present invention so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

DETAILED DESCRIPTION

Various embodiments are disclosed herein for performing mobilitymeasurements, such as a reference symbol power measurement, in acommunication network. One method in a mobile device includes receivinga subframe sequence pattern from a node in the communication network.The subframe sequence pattern indicates types of subframes beingtransmitted by a node in a neighboring cell. The method further includesreceiving a subframe from a sequence of subframes transmitted by theneighboring cell node in the neighboring cell, and determining that thereceived subframe is a multicast subframe based on the subframe sequencepattern. The method then includes performing a single cell-specificreference symbol measurement in response to determining that thereceived subframe is the multicast subframe.

FIG. 1 is a system diagram of a communication network in accordance withsome embodiments. The communication network 100 comprises a plurality ofcells 110, 112, and 114. The cell 110 includes a node 102 and a mobiledevice 108 that is communicatively coupled to the node 102. Similarly,each cell in the communication network 100 comprises a node and at leastone mobile device electrically connected to the node. For example, thecell 112 includes a node 104 and the cell 114 includes a node 106.

The cell 110 in which the mobile device 108 resides is known as servingcell, and the node 102 in such a serving cell is known as serving cellnode. Similarly, the cells 112 and 114 adjacent to the serving cell 110are known as neighboring cells and the nodes 104 and 106 in suchneighboring cells are known as neighboring cell nodes. Note that whileFIG. 1 illustrates physically separate nodes, some or all of the nodesmay also be co-located. For example, each cell node may comprise asector of a multi-sector cell site.

In one embodiment, the cells 110-114 may support a multimediabroadcast/multicast service (MBMS). The MBMS is a service in which themultimedia subframes may be broadcast or multicast in the communicationnetwork 100. The network that supports MBMS via time-synchronousco-frequency transmission may be known as a multicast broadcast singlefrequency network (MBSFN).

In the communication network 100, the nodes 102-106 may transmitsubframes to the mobile device/terminal 108 in either unicast mode ormulticast mode. The mode in which the subframes are transmitted from onenode in the network 100 to a single mobile device is known as unicastmode and the transmission of such subframes is known as unicasttransmission. Similarly, the mode in which subframes bearing the samecontent are transmitted by at least one, and more likely a plurality ofnodes in the communication network 100 to at least one mobile device,and likely many mobile devices simultaneously, is known as multicastmode and the transmission of such subframes is known as multicasttransmission. Also, such a group of nodes is known as a multicast group.Further, the subframe transmitted in a unicast mode is known as aunicast subframe, and the subframe transmitted in a multicast mode isknown as a multicast subframe.

Typically, in an evolved universal mobile telecommunication systemterrestrial radio access network (EUTRAN) configured to support MBMS, aplurality of subframes is transmitted in a sequence from one or morenodes, e.g., the multicast group of nodes, to one or more mobile devicesin the communication network 100. The sequence of such subframestransmitted by the multicast group is known as a subframe sequencepattern or more simply subframe sequence. Each node has a subframesequence pattern that indicates types of subframes being transmitted andthe position of such subframes in the sequence of subframes transmittedby the node. For example, the subframe sequence pattern may be a patternof a sub-sequence of 4 multicast subframes followed by a sub-sequence of6 unicast subframes, or some longer, more irregular sequence.

In one embodiment, the mobile device 108 establishes a communicationlink known as uplink/downlink for communicating data between the nodeand the mobile device 108. The embodiment is described from theperspective of mobile device 108. The embodiment described herein isapplicable to any mobile device in the communication network 100 and notlimited to the mobile device 108. The mobile device 108 initiallyregisters with the communication network 100 by establishing acommunication link with the serving node 102 in the serving cell 110.The established communication link would be strong when the mobiledevice 108 is located nearer to the serving cell node 102. Further, thecommunication link weakens as the mobile device 108 travels to the edgeof the serving cell 110 and may not have continuous communication withthe serving cell node 102. The mobile device 108 thus attempts toestablish a new communication link with a neighboring cell node in theneighboring cells. The process of establishing such a link with theneighboring cell node is known as a handoff process or procedure.

The mobile device 108 prior to establishing the new communication link,performs mobility measurements on the neighboring cells, and may reportsuch measurements to the network for further processing. Such mobilitymeasurements may include an estimate of the received power level in eachof the neighboring cells 112, 114, or an estimate of the power level ofpilot or reference symbols made available by the neighboring cell,although other measurements such as reference symbol signal-to-noiseratio or reference symbol signal-to-noise-plus-interference ratio arealso applicable. The mobile device 108 then selects the neighboring cell112 that has an optimal measurement report, such as a maximum powerlevel. In this case, the measured power level indicates the signalstrength in the neighboring cell 112. The mobile device 108 performssuch power measurement by measuring the power level in a sequence ofsubframes received from each of the neighboring cell nodes 104,106 inthe communication network 100. Specifically, the mobile device 108performs such power measurement in each subframe by measuring power ineach of the reference symbols, and computing a linear average of suchmeasured power over the entire subframe. The process of such powermeasurement using reference symbols is known as reference symbolreceived power measurement (RSRP). Other applicable mobilitymeasurements include reference symbol signal-to-noise ratio (RS-SNR) orreference symbol signal-to-interference-plus-noise ratio (RS-SINR).

In an embodiment, the mobile device 108 in the communication network 100may be a wireless device, a mobile station, a user-equipment, or anysimilar device that can transmit and receive signals. In an embodiment,the mobile device 108 is configured to operate according to any of anumber of different 2G, 3G and 4G wireless communication technologies.These include Global System for Mobile Communication (GSM), CodeDivision for Multiple Access (CDMA), Universal Mobile TelecommunicationSystem (UMTS), Wideband Code Division for Multiple Access (W-CDMA),Orthogonal Frequency Division Multiplexing (OFDM), Single CarrierFrequency Division Multiple Access (SC-FDMA), Discrete FourierTransform-Spread Orthogonal Frequency Division Multiplexing (DFT-SOFDM),Interleaved Frequency-Division Multiple Access (IFDMA), WorldwideInteroperability for Microwave Access (WiMax), Long-Term Evolution (LTE)and other communication technologies.

In an embodiment, the nodes 102-106 establish communication with each ofthe mobile devices in the respective cell area 110-114. The nodes102-106 transmit and receive signals from different mobile devices andinfrastructure components (not shown) that provide wirelesscommunication to the mobile devices. The nodes 102-106 may include aswitching center that establishes a communication session between themobile devices or with the mobile devices in another network. The nodemay be a base station, an access point, an evolved node B (eNB) or anysimilar device that transmits subframes in the communication network100.

In one embodiment, the serving cell node 102 has a list of neighboringnodes known as a neighboring list or neighbor list. The serving cellnode 102 establishes communication with each of the neighboring cellnodes 104, 106 in the neighboring list, and exchanges a subframesequence pattern with the neighboring cell nodes 104, 106, possible viaanother network entity such as a multimedia gateway (not shown), ormobility management entity (not shown). The subframe sequence patternprovides information on the sequence of subframes being transmitted bythe neighboring nodes. Information may be the types of subframestransmitted, and the position of such subframes in the sequence ofsubframes transmitted by each neighboring cell node. Note that in thisembodiment, subframe patterns may be cell-specific, may simply indicatethat no multicast subframes are transmitted, or that all subframes aremulticast subframes except for those subframes not permitted to bemulticast, such as those bearing physical broadcast channel (PBCH) orSynchronization Channel (SCH) transmissions. The serving cell node 102then transmits the subframe sequence pattern of each neighbor cell tothe mobile device 108 which is later utilized by the mobile device 108for measuring the power level or RSRP or RS-SINR of each neighboringcell. The transmission by the serving cell node 102 may be in the formof a broadcast or common control transmission or a dedicated controltransmission.

An actual network may be significantly more complex and may includevarious additional known entities, such as base site controllers,billing, authorization, authentication, and voice mail servers that arenot directly relevant to the present discussion. It is possible thatneighboring networks may operate using the same or differentcommunication technologies. The embodiments described focus onestablishing communication between mobile device 108 and the nodes102-106.

Operationally, the serving cell node 102 receives a subframe sequencepattern from the neighboring cell node 104. The received subframesequence pattern may be independent of a subframe sequence pattern ofthe serving cell node 102. The serving cell node 102 then transmits thereceived subframe sequence pattern to the mobile device 108 that islocated at the edge of the serving cell 110 and tends to move to theneighboring cell 112.

In one embodiment, the mobile device 108 may receive the subframesequence pattern directly from the neighboring cell node 104 over thecontrol channels such as a broadcast control channel (BCH), or amulticast control channel (MCCH) in the neighboring cell 112. In anotherembodiment, the mobile device 108 receives a single bit signal thatindicates a type of transmission mode of the neighboring cell node 104.The signal bit signal is received directly over a control channel suchas a physical broadcast channel (PBCH), from the serving cell node 102.

At the other end, the mobile device 108 receives the subframe sequencepattern of the neighboring cell node 104 and stores such subframesequence pattern in a memory/database of the mobile device 108. Further,the mobile device 108 receives a subframe from a sequence of subframesbeing transmitted by the neighboring cell node 104 in the neighboringcell 112. The mobile device 108 then determines the type of subframereceived based on the stored subframe sequence pattern of thecorresponding neighboring cell node 104. The mobile device 108 finallyperforms mobility measurements such as power or RSRP or RS-SINRmeasurements for the received subframe based on the type of subframedetermined by the mobile device 108. Specifically, the mobile device 108performs mobility measurements for only one reference symbol(RS)-bearing OFDM symbol if the determined subframe is a multicastsubframe, and performs power measurement for up to four RS-bearing OFDMsymbol if the determined subframe is a unicast subframe.

FIG. 2 is a multi-level framing structure 200 in accordance with someembodiments. In this example, the multi-level framing structure 200comprises a sequence of subframes 202. The sequence of subframes 202 isa combination of a subsequence of multicast subframes 204 and asubsequence of unicast subframes 206. For example, in FIG. 2, thesequence of subframes comprises 1 unicast subframe, followed by asubsequence of 4 multicast subframes, followed by a subsequence of 5unicast subframes. In another embodiment, the sequence of subframes mayhave a complete sequence of unicast subframes or a mixed sequence ofunicast and multicast subframes. In one possible implementation of thismulti-level framing structure 200 in a 3GPP LTE communication network,each subframe comprises 2 slots, and each slot comprises a block of 6 or7 orthogonal frequency division multiplexing (OFDM) symbols. The numberof OFDM symbols per slot is determined in combination with the cyclicprefix (CP) length of each OFDM symbol and where the number of OFDMsymbols per slot for unicast and multicast subframes need not beidentical. In one example, multicast subframes comprise 6 OFDM symbolsper subframe and unicast subframes comprise 7 OFDM symbols per subframe,although other combinations are possible. Each multicast subframe maycomprise a time-division multiplexed (TDM) subset of OFDM symbols whichare unicast by each node, and a subset which are multicast by amulticast group of nodes.

In one embodiment, the multicast subframe 208 comprises only 1 unicastRS-bearing OFDM symbol from which the power level or RSRP or RS-SNR orRS-SINR in the neighboring cell node is measured. The RS-bearing OFDMsymbol is located in the first slot of the multicast subframe 208.Similarly, the unicast subframe 228 comprises two slots 216, 218 andeach slot comprises at least 2 RS-bearing OFDM symbols. The firstRS-bearing OFDM symbol (RS1) is located in the first OFDM symbolposition of each of the slots 216, 218 and the second RS-bearing OFDMsymbol (RS2) is located in the fifth OFDM symbol position of each of theslots 216, 218 of the unicast subframe 228. The RS-bearing OFDM symbolsare generally used for decoding the received subframes at the mobiledevice, e.g., by assisting in executing channel estimation etc. However,during mobility of the mobile device 108, the RS-bearing OFDM symbolsare used for performing mobility measurements such as power, RSRP orRS-SINR measurements in the neighboring cell from which the subframe isreceived. The process of measuring power from the RS symbols in thereceived subframe is known as reference symbol received power (RSRP)measurement. Thus, the unicast subframe comprises 2 RS-bearing OFDMsymbols in each slot and has a total of 4 RS-bearing OFDM symbols.

In one embodiment, the sequence of subframes 202 is of 10 milliseconds(ms) in length and may be divided into 10 subframes each of which are 1ms in time duration. Each of the 10 subframes may be further sub-dividedinto 2 slots each of which are 0.5 ms in time duration.

In another embodiment, each slot in a subframe comprises 6 or 7 OFDMsymbols known as block of OFDM symbols. In the case of a 7 OFDM symbolsblock, the first OFDM symbol and the fifth OFDM symbol compriseRS-bearing OFDM symbols from which the mobility measurements such aspower level in the subframe is measured. Thus, a frame of 1 ms timeduration comprises 10 subframes of each 1 ms time duration and 20 slotsof each 0.5 ms time duration.

In some embodiments, the neighboring cell node 112 transmits a subframesequence pattern to the serving cell node 102. The subframe sequencepattern indicates a sequence pattern of subframes, shown in FIG. 2,transmitted by the neighboring cell node 112. The subframe sequencepattern provides information such as type of subframes transmitted bythe neighboring cell node and the position of such subframes in thesequence. For example, the subframe sequence pattern“US-MS-MS-MS-MS-US-US-US-US-US” indicates that the first subframe in thesequence is a unicast subframe, next 4 subframes in the sequence aremulticast subframes, and the last 5 subframes are unicast subframes. Thesubframe sequence pattern is not limited to the one shown in the aboveexample.

In one embodiment, the serving cell node 102 may forward the receivedsubframe sequence pattern to the mobile device 108 that resides at theedge of the serving cell 110. In another embodiment, the mobile device108 may receive the subframe sequence pattern directly from theneighboring cell node 104. At the other end, the mobile device 108utilizes the subframe sequence pattern to determine the type of subframefrom a sequence of subframes received from the neighboring cell node 104and accordingly measures the power level in the received subframe. Forexample, if the received subframe is a multicast subframe then the powerlevel is measured from only 1 RS-bearing OFDM symbol in the subframe. Onthe other hand, if the received subframe is a unicast subframe then thepower level is measured from up to 4 RS-bearing OFDM symbols in thesubframe.

In another embodiment, the serving cell node 102 may receive from eachneighboring cell, subframe sequence pattern information corresponding toeach carrier frequency supported by each neighboring cell. The servingcell node 102 then transmits carrier frequency specific subframesequence pattern information to the mobile device 108, which is laterused for performing inter-frequency mobility measurements.

In one embodiment, the serving cell node 102 may determine, uponreceiving subframe sequence pattern information from each of theneighboring cells 112,114, that none of the neighboring cells 112, 114is transmitting multicast subframes or at least one neighboring cell 112is transmitting multicast frames. In such an embodiment, thetransmission of cell-specific subframe sequence patterns to the mobiledevice 108 may be reduced to transmit a single bit signal or a singlebinary indicator directing the mobile device 108 to consider either a)all subframes are unicast, in which case all RS-bearing OFDM symbols inall subframes are available for measurement, or b) at least one subframeis multicast, in which case the mobile device 108 may restrict itsmeasurements to only 1 RS-bearing OFDM symbol in all subframes. Notethat the serving cell node 102 may transmit such a single bit signal ora single binary indicator to the mobile device 108 over each carrierfrequency supported by the communication network 100, or may transmit asingle such binary indicator applicable in common to all carrierfrequencies in the communication network 100.

In another embodiment, the serving cell node 102 receives subframesequence pattern from each of the neighboring cell nodes 104, 106. Uponreceiving such subframe sequence pattern, the serving cell node 102determines that all the neighboring cell nodes 104, 106 are transmittingthe same subframe sequence pattern as that of the serving cell node 102.The serving cell node 102 then modifies the single bit signal or thesingle binary indicator, and transmits the modified single bit signal tothe mobile device 108. The modified single bit signal indicates to themobile device that a) the neighboring cell nodes 104, 106 have samesubframe sequence pattern as that of the serving cell node 102, or b) atleast one neighbour cell node 104 has a different subframe sequencepattern. In the second case (b), the mobile device 108 may restrict itsmeasurements to only 1 RS-bearing OFDM symbol in all subframes receivedfrom the neighboring cell nodes 104, 106. Note that the serving cellnode 102 may transmit such a modified single bit signal or single binaryindicator for each carrier frequency supported by the network 100, ormay transmit a single bit signal applicable in common to all carrierfrequencies in the network 100. In another embodiment, the single bitsignal is transmitted over a control channel such a broadcast controlchannel (BCH) or a multicast control channel (MCCH).

FIG. 3 is a block diagram of a mobile device in accordance with someembodiments of the invention. The mobile device 300 comprises aprocessor 308, a memory 310, a transceiver 304, and an antenna 306 forperforming mobility measurement in the communication network 100.

The memory 310 is a common storage unit that is coupled to the processor308 for storing the subframe sequence pattern received from each node inthe neighboring cells 112, 114. The subframe sequence pattern indicatesthe types of subframes being transmitted by the neighboring cell nodes104, 106. In one embodiment, the subframe sequence may be a sequence ofonly unicast subframes or a combination of unicast and multicastsubframes. In one embodiment, the memory 310 may be embedded within aprocessor 308 or may be placed external to the processor 308. The memory310 maintains a database in which a link is created between the receivedsubframe sequence pattern and an identification associated with thecorresponding neighboring cell node.

The processor 308 coupled between the memory 310 and the transceiver 304operates to perform cell-specific reference symbol power measurementfrom the received subframe. The processor 308, initially, stores thesubframe sequence pattern in the memory 310 coupled therewith, andutilizes such sequence pattern to determine the type of subframereceived from the corresponding neighboring cell node 104. In oneembodiment, the subframe may be a part of the sequence of subframestransmitted by the neighboring cell node 104.

In one embodiment, the processor 308 is configured with two modules, adetermining module 312 and a measuring module 314. The determiningmodule 312 is configured to determine the type of subframe received fromthe neighboring cell node 104. The determining module 312 determines thetype by extracting a sequence number of the received subframe andcomparing the sequence number with the corresponding subframe sequencepattern. For example, the extracted sequence number may be 2 and iscompared with the subframe sequence pattern“US-MS-MS-MS-US-US-US-US-US.” The subframe type at the positionassociated with the number ‘2’ in the subframe sequence pattern is themulticast subframe and thus, the type of subframe received is consideredas the multicast subframe.

The measuring module 314 is configured for performing cell-specificreference symbol measurements such as power measurement or othermobility measurements based on the type of the subframe determined bythe determining module 312. For example, if the subframe determined isas a multicast subframe then a single cell-specific reference symbolpower measurement is performed on RS1 (See FIG. 2, 214.) Similarly, ifthe subframe determined is a unicast subframe then up to fourcell-specific reference symbol power measurements are performed and thencombined, such as by linear averaging. The measuring module 314 performssuch power measurement by measuring power in each reference symbol inthe subframe, and computing a linear average of all the measured powerin the subframe, or other combining means. Thus, accuracy in measuringpower in a unicast subframe is generally higher than measuring power ina multicast subframe.

In another embodiment, to achieve specific measurement accuracy, themobile device 300 may elect to adjust the number of performed referencesymbol measurements to meet the required accuracy. For example, themobile device 300 may use its knowledge that specific subframes are usedfor unicast transmission to exploit the larger number of RS-bearing OFDMsymbol observations available in such subframes. Accordingly, in orderto generate the same total number of RS-bearing OFDM symbolobservations, the mobile device 300 may advantageously schedulemeasurements to coincide with known unicast subframes, and so reduce thetotal number of measured subframes of any type. By so reducing the totalnumber of measured subframes, the mobile device 300 may reduce the totalactivity time of its radio subsystem and other processing elements andso reduce total power consumption or current drain. Alternatively, themobile device 300 may use its knowledge of the occurrence of unicastsubframes to reduce the total number of subframe observations requiredto meet the measurement accuracy for a specific neighboring cell and someasure more neighboring cells per unit time while maintaining the samelevel of accuracy.

In one embodiment, the mobile device 300 is configured with atransceiver 304, which is coupled to the processor 308. The transceiver304 is known and can vary with the communication technology. Thetransceiver 304 operates as a receiver and a transmitter for receivingand transmitting subframes via the antenna 306 from or to the network.In an embodiment, the transceiver 304 operates for receiving andtransmitting subframes from different mobile devices and infrastructurecomponents (not shown) of the network. In an embodiment, the transceiver304 may receive the subframe sequence pattern over a control channel andsends it to the processor 308. In another embodiment, the transceiver304 may receive the single bit signal from the serving cell. Thetransceiver 304 may be a separate transmitter and a receiver operatingindependently for transmitting and receiving signals in thecommunication network, e.g. network 100.

Operationally, the transceiver 304 receives a subframe sequence patternfrom each node in the neighboring cells 112, 114. In one embodiment, thesubframe sequence pattern of the neighboring cell nodes 112, 114 may bereceived from the serving cell node 102 in the serving cell 110. Forexample, the transceiver 304 receives the subframe sequence pattern ofthe neighboring cell node 104 via the serving cell node 102. In anotherembodiment, the subframe sequence pattern may be received directly fromthe neighboring cell nodes 104, 106 in the neighboring cells 112, 114respectively. The subframe sequence pattern is received over a commoncontrol channel such as a BCH, or a MCCH or via a dedicatedtransmission, such as a physical downlink shared channel (PDSCH). Thetransceiver 304 sends the received subframe sequence pattern to theprocessor 308 that is couple therewith.

The processor 308 stores the received subframe sequence pattern in thememory 310. The procedure is repeated for each subframe sequence patternreceived by the transceiver 304 of the mobile device 300.

The processor 308 then receives a subframe from a sequence of subframestransmitted by the neighboring cell node 104. The processor 308 extractsa sequence number from the received subframe and identifies the type ofsubframe present in the subframe sequence pattern at a positionassociated with the sequence number. The processor 308 then determinesthe type of the subframe received based on the identified type in thesubframe sequence pattern. The processor 308 further measures the powerlevel in the received subframe by measuring power from only firstcell-specific RS-bearing OFDM symbol if the received subframe is amulticast subframe, and measuring power from 4 cell-specific RS-bearingOFDM symbols if the received subframe is a unicast subframe.

In one embodiment, the above described procedure is repeated for thesequence of subframes received from each neighboring cell node. Themobile device 300 then determines the neighboring cell that has amaximum power level, reports such data along with other ancillarymeasurement data to the network, and finally may be directed by thenetwork to move to that particular neighboring cell.

FIG. 4 is a flowchart of a method 400 for performing mobilitymeasurements based on a subframe sequence pattern in accordance withsome embodiments of the invention is shown. In an embodiment, the method400 is described from the perspective of a mobile device, e.g. mobiledevice 108 of FIG. 1. The method 400 starts with receiving 402 asubframe sequence pattern from a node in the communication network 100.The node may be a serving cell node 102 in the serving cell 110 or aneighboring cell node 104 in a neighboring cell 112. The subframesequence pattern indicates different types of subframes beingtransmitted by the neighboring cell node 104 in the neighboring cell112. For example, the subframe sequence pattern indicates whether areceived subframe is a unicast subframe or a multicast subframe. Themobile device 108 stores the received subframe sequence pattern andutilizes such stored subframe sequence pattern to identify the type ofsubframe received from the corresponding neighboring cell node 104. Thereceived subframe sequence pattern is independent of a subframe sequencepattern of the serving cell node 102 in the serving cell 110. Forexample, the neighboring cell node 104 in the neighboring cell 112 maynot have the same subframe sequence pattern of the serving cell node 102in the serving cell 110 or of any other neighboring cells.

The method 400 continues with a step of receiving 404 a subframe from asequence of subframes transmitted by the neighboring cell node 104 inthe neighboring cell 112. The sequence of subframe may be a sub-sequenceof unicast subframes and a sub-sequence of multicast subframes. Themethod 400 then continues with a step of determining 406 that thereceived subframe is a multicast subframe based on the correspondingsubframe sequence pattern. A sequence number of the subframe is comparedwith the subframe sequence pattern and the type of subframe, in thesubframe sequence pattern, at a position associated with the sequencenumber is determined. The method then continues with a step ofperforming 408 a single cell-specific reference symbol measurement inresponse to determining that the received subframe is the multicastsubframe. The single cell-specific symbol measurement includes measuringpower of a cell-specific reference symbol in the received subframe, ormeasuring signal-to-noise ratio of a cell-specific reference symbol inthe received subframe.

FIG. 5 is a flow chart of a method for determining a type of subframebased on the subframe sequence pattern in accordance with someembodiments. The method 500 is described with reference to FIG. 1. Themethod 500 described from the perspective of a mobile device, e.g.mobile device 108 of FIG. 1.

The method 500 describes the steps 406 and 408 of FIG. 4 in accordancewith some embodiments. The method 500 begins with the step of extracting502 a sequence number from the received subframe. The extracted sequencenumber indicates a position in the sequence of subframes transmitted bythe neighboring cell node 104. The method 500 continues with a step ofidentifying 504 a type of subframe present, in the subframe sequencepattern, at a position associated with the extracted sequence number.The extracted sequence number of the subframe is compared with thesubframe sequence pattern. The type of subframe present at a positionassociated with the extracted sequence number, in the subframe sequencepattern, is identified.

The method 500 continues with a step of determining 506 whether theidentified type is a multicast type. If the identified type is amulticast type then the method continues with a step of considering 508the received subframe as a multicast subframe. The method 500 thencontinues with a step of performing 510 a single cell-specific referencesymbol measurement in response to determining that the received subframeis the multicast subframe.

On the other hand, if the identified type is a unicast type then themethod 500 continues with a step of considering 512 the receivedsubframe as a unicast subframe. The method then continues with a step ofperforming 514 at least two cell-specific reference symbols measurement.The unicast subframe has 4 RS symbols and thus, measuring power using 4RS symbols may improve the accuracy of power measurement in theneighboring cell. Thus, power measurement is varied according to thetype of subframe received from the neighboring cell node 104.

FIG. 6 is a flowchart of a method for performing mobility measurementsin a communication network based on a single bit signal in accordancewith some embodiments is shown. In an embodiment, the method 600 isdescribed from the perspective of a mobile device, e.g. mobile device108 of FIG. 1. The method 600 starts with receiving 602 a single bitsignal from a serving cell node 102. The single bit signal indicates atype of subframes being transmitted by the neighboring cell node 104 inthe neighboring cell 112. The single bit signal may be transmitted overcommon control channels such as BCH, or MCCH or even using a dedicatedcontrol channel, or may be included in a handover control message.

The method continues with a step of receiving 604 a subframe from asequence of subframes transmitted by the neighboring cell node 104 inthe neighboring cell 112. The subframe received may be a unicastsubframe or a multicast subframe. The unicast subframe has 4 OFDM symbolbearing RS symbols and the multicast subframe has 1 OFDM symbol bearingRS symbols. The OFDM symbol bearing RS symbols may be used forperforming different mobility measurements such as a power, RSRP orRS-SINR measurements for the received subframe.

The method then continues with a step of determining 606 that thereceived subframe is a multicast subframe based on the single bit signalor single binary indicator received from the serving cell node 102. Thesingle bit signal indicates that (a) at least one neighboring cell node104 transmits at least one multicast subframe, or (b) no neighboringcell node transmits at least one multicast subframe. In the first case(a), the mobile device 108 ascertains all the received subframes as themulticast subframes and performs mobility measurement using only singlecell-specific reference symbol. In the second case (b), the mobiledevice 108 ascertains all the received subframes as the unicastsubframes and performs mobility measurement using at least twocell-specific reference symbols.

Further, upon determining 606 that the received subframe is a multicastsubframe, the method 600 continues with a step of performing 608 asingle cell-specific reference symbol measurement. The cell-specificreference symbol measurement may be any kind of mobility measurementsuch as a power, RSRP or RS-SINR measurements.

FIG. 7 is a flow chart of a method for determining a type of subframebased on the single bit signal in accordance with some embodiments isshown. The method 700 is described with reference to FIG. 1. The method700 described from the perspective of a mobile device, e.g. mobiledevice 108 of FIG. 1. The method 700 describes a step 606 of FIG. 6 inaccordance with some embodiments. The method 700 begins with a step ofextracting 702 a binary value from the received single bit signal. Thebinary value indicates the type of subframes transmitted by theneighboring cell nodes 104, 106.

The method 700 then continues with a step of determining 704 whether theextracted binary value is a first binary value. If the extracted binaryvalue is a first binary value, e.g., ‘1’, then the method continues witha step of considering 706 at least one neighboring cell node 104transmits at least one multicast subframe. The first binary valueindicates to the mobile device that the neighboring cell nodes maytransmit multicast subframes and accordingly informs the mobile deviceto perform mobility measurement by using only single cell-specificreference symbol for all the subframes received from the neighboringcell nodes 104, 106.

The method 700 then continues with a step of ascertaining 708 that thereceived subframe is the multicast subframe in response to consideringat least one neighboring cell node transmits at least one multicastsubframe.

On the other hand, at step 704, if the binary value is not a firstbinary value or the binary value is a second binary value then themethod 700 continues with a step of considering 710 no neighboring cellnode transmits at least one multicast subframe. The second binary value,e.g., ‘0’, indicates to the mobile device that no multicast subframesare transmitted by the neighboring cell nodes 104, 106 and accordinglyinforms the mobile device to perform mobility measurement using at leasttwo cell-specific reference symbols for all the subframes received fromthe neighboring cell nodes 104, 106. Thus, the type of subframesreceived from the neighboring cell nodes 104, 106 is determined based onthe binary value present in the single bit signal received by the mobiledevice 108.

In an alternate embodiment, the serving cell node 102 may receivesubframe sequence pattern from each of the neighboring cell nodes 104,106. If the received subframe sequence pattern is same as a subframesequence pattern of the serving cell node 102, the serving cell node 102modifies the binary value in the single bit signal. Further, themodified single bit signal is transmitted to the mobile device toindicate that the subframe sequence pattern is same for all the cellnodes 104, 106 in the communication network 100. The mobile device thenperforms mobility measurements by considering a common subframe sequencepattern for all the subframes received from the neighboring cell nodes104, 106 in the communication network 100. In one embodiment, thetransmitted single bit signal is associated with each of at least twocarrier frequencies in the communication network 100.

In the foregoing specification, specific embodiments have beendescribed. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of present teachings. The benefits,advantages, solutions to problems, and any element(s) that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as a critical, required, or essential features orelements of any or all the claims. The invention is defined solely bythe appended claims including any amendments made during the pendency ofthis application and all equivalents of those claims as issued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has”,“having,” “includes”, “including,” “contains”, “containing” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises, has,includes, contains a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. An element proceeded by“comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . .a” does not, without more constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises, has, includes, contains the element. The terms“a” and “an” are defined as one or more unless explicitly statedotherwise herein. The terms “substantially”, “essentially”,“approximately”, “about” or any other version thereof, are defined asbeing close to as understood by one of ordinary skill in the art, and inone non-limiting embodiment the term is defined to be within 10%, inanother embodiment within 5%, in another embodiment within 1% and inanother embodiment within 0.5%. The term “coupled” as used herein isdefined as connected, although not necessarily directly and notnecessarily mechanically. A device or structure that is “configured” ina certain way is configured in at least that way, but may also beconfigured in ways that are not listed.

It will be appreciated that some embodiments may be comprised of one ormore generic or specialized processors (or “processing devices”) such asmicroprocessors, digital signal processors, customized processors andfield programmable gate arrays (FPGAs) and unique stored programinstructions (including both software and firmware) that control the oneor more processors to implement, in conjunction with certainnon-processor circuits, some, most, or all of the functions of themethod and/or apparatus described herein. Alternatively, some or allfunctions could be implemented by a state machine that has no storedprogram instructions, or in one or more application specific integratedcircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic. Of course, acombination of the two approaches could be used.

Moreover, an embodiment can be implemented as a computer-readablestorage medium having computer readable code stored thereon forprogramming a computer (e.g., comprising a processor) to perform amethod as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, a CD-ROM, an optical storage device, a magnetic storagedevice, a ROM (Read Only Memory), a PROM (Programmable Read OnlyMemory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM(Electrically Erasable Programmable Read Only Memory) and a Flashmemory. Further, it is expected that one of ordinary skill,notwithstanding possibly significant effort and many design choicesmotivated by, for example, available time, current technology, andeconomic considerations, when guided by the concepts and principlesdisclosed herein will be readily capable of generating such softwareinstructions and programs and ICs with minimal experimentation.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various embodiments for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus the following claims arehereby incorporated into the Detailed Description, with each claimstanding on its own as a separately claimed subject matter.

1. A method in a mobile device for performing mobility measurements in acommunication network, the method comprising: receiving a subframesequence pattern from a node in the communication network, the subframesequence pattern indicates types of subframes being transmitted by aneighboring cell node in a neighboring cell, wherein the types ofsubframes includes a unicast subframe comprising four cell-specificorthogonal frequency division multiplexing (OFDM) symbols bearingreference symbols, and a multicast subframe comprising one cell-specificOFDM symbol bearing reference symbols; receiving a subframe from asequence of subframes transmitted by the neighboring cell node in theneighboring cell; determining that the received subframe is themulticast subframe based on the subframe sequence pattern; andperforming a single cell specific reference symbol measurement inresponse to determining that the received subframe is the multicastsubframe.
 2. The method of claim 1 further comprising: performing asingle cell-specific reference symbol measurement in response todetermining that the received subframe is the multicast subframe;determining that the received subframe is the unicast subframe based onthe subframe sequence pattern; and performing at least two cell-specificreference symbols measurement in response to determining that thereceived subframe is the unicast subframe.
 3. The method of claim 1,wherein receiving the subframe sequence pattern comprises receiving thesubframe sequence pattern from a serving cell node in a serving cell,wherein the serving cell is a cell in which the mobile device iscurrently located.
 4. The method of claim 1, wherein receiving thesubframe sequence pattern comprises receiving the subframe sequencepattern from the neighboring cell node in the neighboring cell.
 5. Themethod of claim 1, wherein the subframe sequence pattern is receivedover a broadcast control channel (BCH) or a multicast control channel(MCCH).
 6. The method of claim 1, wherein the subframe comprises atleast one reference symbol in a first slot of a plurality of slots inthe subframe.
 7. The method of claim 1, wherein the subframe sequencepattern indicates a sequence pattern of unicast and multicast subframestransmitted by the neighboring cell node in the neighboring cell.
 8. Amethod in a mobile device for performing mobility measurements in acommunication network, the method comprising: receiving a subframesequence pattern from a node in the communication network, the subframesequence pattern indicates types of subframes being transmitted by aneighboring cell node in a neighboring cell; receiving a subframe from asequence of subframes transmitted by the neighboring cell node in theneighboring cell; determining that the received subframe is a multicastsubframe based on the subframe sequence pattern extracting a sequencenumber from the received subframe, wherein the sequence number indicatesa position in the sequence of subframes transmitted by the neighboringcell node; identifying a type of subframe present, in the subframesequence pattern, at a position associated with the extracted sequencenumber; considering the received subframe as the multicast subframe whenthe identified type is a multicast type; and considering the receivedsubframe as a unicast subframe when the identified type is a unicasttype.
 9. The method of claim 2, wherein performing the singlecell-specific reference symbol measurement comprises measuring power ofa cell-specific reference symbol in the received subframe.
 10. Themethod of claim 2, wherein performing the single cell-specific referencesymbol measurement comprises measuring signal-to-noise ratio of acell-specific reference symbol in the received subframe.
 11. The methodof claim 3, wherein the received subframe sequence pattern isindependent of a subframe sequence pattern of the serving cell node inthe serving cell.
 12. A method in a mobile device for performingmobility measurements in a communication network, the method comprising:receiving a single bit signal from a serving cell node in a servingcell, wherein the single bit signal indicates a type of subframes beingtransmitted by at least one neighboring cell node in a plurality ofneighboring cells, wherein the types of subframes includes a unicastsubframe comprising four cell-specific orthogonal frequency divisionmultiplexing (OFDM) symbols bearing reference symbols, and a multicastsubframe comprising one cell-specific OFDM symbol bearing referencesymbols; receiving a subframe from a sequence of subframes transmittedby the neighboring cell node; determining that the received subframe isthe multicast subframe based on the received single bit signal; andperforming a single cell specific reference symbol measurement inresponse to determining that the received subframe is the multicastsubframe.
 13. The method of claim 12 further comprising: performing asingle cell-specific reference symbol measurement in response todetermining that the received subframe is the multicast subframe;determining that the received subframe is the unicast subframe based onthe received single bit signal; and performing at least twocell-specific reference symbols measurement in response to determiningthat the received subframe is the unicast subframe.
 14. The method ofclaim 12, wherein determining that the received subframe is themulticast subframe comprises: extracting a binary value from thereceived single bit signal; considering at least one neighboring cellnode transmits at least one multicast subframe when the extracted binaryvalue is a first binary value; ascertaining that the received subframeis the multicast subframe in response to considering at least oneneighboring cell node transmits at least one multicast subframe.
 15. Themethod of claim 13, wherein determining that the received subframe isthe unicast subframe comprises: extracting a binary value from thereceived single bit signal; considering no neighboring cell nodetransmits at least one multicast subframe when the extracted binaryvalue is a second binary value; ascertaining that the received subframeis the unicast subframe in response to considering no neighboring celltransmits at least one multicast subframe.
 16. The method of claim 12,wherein the single bit signal is received over a control channel. 17.The method of claim 12, wherein the single bit signal indicates that asubframe sequence pattern of each neighboring cell node is same as asubframe sequence pattern of the serving cell node.
 18. The method ofclaim 12, wherein the received single bit signal is associated with eachof at least two carrier frequencies in the communication network. 19.The method of claim 13, wherein performing the single cell-specificreference symbol measurement comprises measuring power of a firstreference symbol in the received subframe when the received subframe isthe multicast subframe, the measured power indicating a power level inthe neighboring cell.
 20. An apparatus in a mobile device for performingmobility measurements in a communication network, the apparatuscomprising: a transceiver configured to receive a subframe sequencepattern from a node in the communication network, wherein the subframesequence pattern indicates types of subframes being transmitted by aneighboring cell node in a neighboring cell, further wherein the typesof subframes includes a unicast subframe comprising four cell-specificorthogonal frequency division multiplexing (OFDM) symbols bearingreference symbols, and a multicast subframe comprising one cell-specificOFDM symbol bearing reference symbols; and to receive a subframe from asequence of subframes transmitted by the neighboring cell node in theneighboring cell, wherein the subframe comprises at least onecell-specific reference symbol; and a processor, coupled to thetransceiver, configured to determine that the received subframe is themulticast subframe based on the subframe sequence pattern, and toperform a single cell specific reference symbol measurement in responseto determining that the received subframe is a multicast subframe. 21.The apparatus of claim 20, wherein the processor is further configuredto perform a single cell-specific reference symbol measurement inresponse to determining that the received subframe is a multicastsubframe, and to determine that the received subframe is the unicastsubframe based on the subframe sequence pattern; and to perform at leasttwo cell-specific reference symbols measurement in response todetermining that the received subframe is the unicast subframe.